Castor, Mountain summit between Valais, Switzerland and Aosta Valley, Italy.

Castor is a 4225-meter summit in the Pennine Alps on the Swiss-Italian border, separated from Pollux by the Zwillingsjoch (3846 m) and from the Western Lyskamm by the Felikjoch (4061 m). Its long, narrow southeast ridge rises from the Felik Glacier, while the west flank above the Grande Ghiacciaio di Verra is used from the Swiss side.

The first recorded ascent took place in 1861 when F.W. Jacomb and William Mathews summited with guide Michel Croz. This climb helped establish the mountain as a recognized route in the climbing community.

Castor and Pollux are named after the Dioscuri, the twin brothers of Greek mythology; the German article notes the naming follows the Greek pair, and the Italian source says the shape is best seen from the Swiss north side. The two summits are separated by the Zwillingsjoch (Passo di Verra, 3846 m).

Climbers can begin from Klein Matterhorn on the Swiss side or approach via Capanna Quintino Sella hut from the Italian side. Snow, ice, and rock climbing gear are necessary, with stable weather being critical for safe passage.

The Felikjoch, separating Castor from the Western Lyskamm, is given as 4061 m in the Italian source and 4068 m elsewhere; the Zwillingsjoch (Passo di Verra) between Castor and Pollux is 3845 m. The Italian-Swiss border runs along the ridge from Pollux over Castor to the Lyskamm, except at the Felikhorn, whose summit lies in Italy.